The present invention relates to a driving circuit of thin-film transistor electroluminescent (TFT-EL) display and the operation method thereof, and more particularly to a driving circuit for driving a light-emitting diode (LED) in TFT-EL display and its operation method.
Rapid advances in flat-panel display (FPD) technologies have made high quality large-area, full-color, high-resolution displays possible. These displays have enabled novel applications in electronic products such as lap top computers and pocket-TVs. Liquid crystal display (LCD) is the fastest one of developing these FPD technologies.
These LCD panels use thin-film-transistors (TFT) as an active-addressing scheme, which relaxes the limitations in direct addressing. The success of LCD technology is in large part due to the rapid progress in the fabrication of large-area TFT substrate. The almost ideal match between TFT switching characteristics and other LCD display elements also plays a key role.
A major drawback of TFT-LCD panels is that they require bright backlighting. This is because the transmittance of the TFT-LCD is poor, particularly for colored panels. Power consumption for backlighted TFT-LCD panels is considerable, and this adversely affects portable display applications.
Moreover, backlighting also increases the entire thickness of the flat panel, for example, using a typical fluorescent tube lamp, the additional thickness is about xc2xe to 1 inch. Backlight also adds extra weight to the FPD.
An ideal solution to the foregoing limitation would be a low power emissive display that eliminates the need for backlighting. A particularly attractive candidate is the thin-film-transistor-electroluminescent (TFT-EL) display. In the TFT-EL display, the individual pixels can be addressed to emit light and auxiliary backlighting is not required.
Referring to FIG. 1, a circuit for driving an organic light-emitting diode (OLED) in a TFT-EL display is shown. In the circuit, the OLED is controlled with two thin-film transistors and one capacitor. When the scan line is driven, the transistor T1 is switched on and the signal from the data line is input into a capacitor C. After the capacitor C is charged, a current source Vsupply supplies a current to drive an organic light-emitting diode (OLED) D according to the I-V characteristic of transistor T2 and the voltage level of the capacitor C. However, even with the same data signal, due to the variance of the I-V characteristic between the individual transistors in the actual manufacturing process, it is hard to control the luminescence uniformity of individual pixels.
The present invention provides a circuit for driving a light-emitting diode (LED) in a thin-film transistor electroluminescent (TFT-EL) display and the operation method thereof. The circuit including two transistors is used to control the luminescent intensity of the LED. A scan line and a discharge line are used to respectively control the transistors, and such transistors determine charge/discharge of both the capacitor and the LED. Additionally, the LED emits by means of a current through the channel of the transistor when the capacitor is discharged.
The present invention provides a circuit for driving a light-emitting diode (LED) in a thin-film transistor electroluminescent (TFT-EL) display which comprises a data line, a scan line, a discharge line, a capacitor, a lightemitting diode, a first transistor and a second transistor. The first transistor is composed of a first gate electrode, a first source electrode, and a first drain electrode, wherein the first gate electrode is connected to the scan line, the first source electrode is connected to the data line, and the first drain electrode is connected to the capacitor. The second transistor consists of a second gate electrode, a second source electrode, and a second drain electrode, wherein the second gate electrode is connected to the discharge line, the second source electrode is connected to the capacitor and the second drain is connected to the light-emitting diode.
The present invention also provides a method for driving an LED in a TFT-EL display. The method comprises the following steps. A scan signal switches on a first transistor. A charging step is performed thereafter to charge a capacitor from a data line through said first transistor. A discharge signal switches on a second transistor. And, a discharging step is performed thereafter to drive said LED by discharging said capacitor through said second transistor.